High frequency-weldable articles and method for connecting the same

ABSTRACT

High frequency-weldable articles, such as sheets or yarns, include at least one high frequency-weldable part that is made from a modified polyethylene terephthalate (PET) material and that has a melting point ranging from 100° C. to 250° C. The modified PET material is prepared from a composition that includes terephthalic acid, ethylene glycol and a diol modifier. The diol modifier is selected from the group consisting of neopentanediol, 1,3-dihydroxy-2-methylpropane, 1,3-dihydroxy-2-methylpropane alkoxylate, 2,5-dimethyl-2,5-hexanediol, polyethylene glycol, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Taiwanese application no. 093117582,filed on Jun. 18, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to high frequency-weldable articles, such assheets, fibers, and yarns, and particularly to high frequency-weldablearticles that include at least one high frequency-weldable part madefrom a modified polyethylene terephthalate material. This invention alsorelates to a method for connecting the high frequency-weldable articlesthrough high frequency welding techniques.

2. Description of the Related Art

Some articles of thermoplastic materials that possess a loss factorproperty, such as plastic sheets that are made from polyethylene andpolypropylene and that are used in food packaging, and filters of airconditioners that are made from polyvinyl chloride or polyurethane, canbe laminated quickly and evenly through high frequency weldingtechniques without using solder material. However, since the use ofthese halogen-containing materials, such as polyvinyl chloride, will berestricted due to environmental concerns, the relevant industries haveattempted to develop high frequency-weldable packaging sheets and fiberfilters that are made from halogen-free thermoplastic materials.

Polyethylene terephthalate (PET) is a halogen-free and inexpensivesaturated ester that is commercially available and that has a wide rangeof applications. However, since pure PET has no loss factor property,the articles, such as the plastic sheets, fibers or fiber articles, madetherefrom are not suitable for use with high frequency weldingtechniques.

In recent years, modification of PET and manufacture of PET articleshave been focal points in the art of polymers. U.S. Pat. No. 5,585,177discloses a laminate including a triple layered thermoplastic resinlaminated on one or both sides of a metal sheet. The inner layer, whichis proximate to the metal sheet, and the outer layer of the triplelayered thermoplastic resin are made from modified polyesters.Preferably, the inner and outer layers may be made from isophthalic acid(IPA)-modified PET. Alternatively, the inner layer may be made from ablended polyester resin that is prepared by blending a pure PET (meltingpoint: 256° C.) and a butylene glycol-modified PET (melting point: 252°C.) in equal amounts. However, inclusion of the metal substrate resultsin a higher production cost and difficulty when recycling the laminate.

U.S. Pat. No. 6,551,699 discloses a calendered sheet made from acalendering composition comprising a modified polyester and a fattyester. The modified polyester is 1,4-cyclohexanedimethanol(CHDM)-modified PET. The crystallization half time of PET may beprolonged through modification of 1,4-cyclohexane-dimethanol so as tofavor the calendering operation. However, the modified polyester canonly be dried at a temperature lower than 70° C. When pellets of themodified polyester are processed to form desired articles, a lengthytime for drying or pre-crystallizing the pellets of the modifiedpolyester is required, which results in an increase in the manufacturingcosts.

U.S. Pat. No. 5,804,025 discloses a shaped structure made from amodified polyester through high frequency welding techniques. The shapedstructure is in the form of a high frequency-weldable staple fiber webthat consists of a first fiber and a second fiber. The first fiber ismade from PET modified with 33 mol % IPA.

Conventionally, the modified PET is normally produced by addition ofbivalent acids, particularly IPA, during polymerization of PET. When IPAis not added to PET in a sufficient amount, such as less than 33 mol %,the modified PET thus made, in spite of being suitable for use in theproduction of high frequency-weldable thermoplastic sheets, cannot bespun into high frequency-weldable yarns. In other words, the applicationof the modified PET thus formed is limited.

As the demand for packaging sheets and fiber products is relativelylarge, there remains a need in the art to improve the highfrequency-weldable sheet or fiber product, such as yarn, that is madefrom a halogen-free, inexpensive modified PET.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a highfrequency-weldable sheet or yarn that can overcome the aforesaiddrawbacks of the prior art.

Another object of this invention is to provide a method for connectingfirst and second parts, each of which has a high frequency-weldableportion made from a modified PET material, through high frequencywelding techniques.

According to one aspect of the present invention, a highfrequency-weldable sheet includes a substrate, and a highfrequency-weldable layer formed on the substrate and made from amodified PET material that is prepared from a composition includingterephthalic acid, ethylene glycol and a diol modifier. The diolmodifier is selected from the group consisting of neopentanediol,1,3-dihydroxy-2-methylpropane, 1,3-dihydroxy-2-methylpropane alkoxylate,2,5-dimethyl-2,5-hexanediol, polyethylene glycol, and combinationsthereof. The high frequency-weldable layer has a melting point rangingfrom 100° C. to 250° C.

According to another aspect of the present invention, a highfrequency-weldable yarn includes fibers composed of a highfrequency-weldable material that is made from a modified PET materialthat is prepared from a composition including terephthalic acid,ethylene glycol and a diol modifier. The diol modifier is selected fromthe group consisting of neopentanediol, 1,3-dihydroxy-2-methylpropane,1,3-dihydroxy-2-methylpropane alkoxylate, 2,5-dimethyl-2,5-hexanediol,polyethylene glycol, and combinations thereof. The highfrequency-weldable yarn has a melting point ranging from 100° C. to 250°C.

According to yet another aspect of the present invention, a method forconnecting first and second parts includes the steps of: (a) preparingthe first and second parts in such a manner that each of the first andsecond parts has a portion composed of a high frequency-weldablematerial that is made from a modified PET material prepared from acomposition including terephthalic acid, ethylene glycol and a diolmodifier, the diol modifier being selected from the group consisting ofneopentanediol, 1,3-dihydroxy-2-methylpropane,1,3-dihydroxy-2-methylpropane alkoxylate, 2,5-dimethyl-2,5-hexanediol,polyethylene glycol, and combinations thereof; (b) applying highfrequency electromagnetic radiation to the portions of the first andsecond parts so as to melt the portions of the first and second parts;and (c) joining the melted portions of the first and second parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments of this invention, with reference to the accompanyingdrawings, in which:

FIG. 1 is a fragmentary perspective view to illustrate the preferredembodiment of a high frequency-weldable sheet according to thisinvention;

FIG. 2 is a fragmentary perspective view to illustrate the firstembodiment of a high frequency-weldable yarn according to thisinvention;

FIG. 3 is a fragmentary perspective view to illustrate the secondembodiment of a high frequency-weldable yarn according to thisinvention; and

FIG. 4 is a fragmentary perspective view to illustrate how two highfrequency-weldable sheets are interconnected according to a method forconnecting two parts of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In view of the foregoing, the applicant of this invention appreciatedthat a modified PET material can be used in the manufacture of a highfrequency-weldable sheet or yarn. The resultant high frequency-weldablesheet or yarn of this invention is free from undesired formation ofcrystalline in welding area, as commonly encountered during highfrequency welding of the conventional modified PET material.Particularly, the modified PET material is modified by addition ofspecific species of diols and control of the diol amount used duringpolymerization of the composition for preparing the modified PETmaterial.

Referring to FIG. 1, the high frequency-weldable sheet 1 according tothis invention includes a substrate 10, and a first highfrequency-weldable layer 11 formed on the substrate 10 and made from amodified PET material that is prepared from a composition includingterephthalic acid, ethyleneglycol and a diol modifier.

The melting point of the first high frequency-weldable layer 11 rangesfrom 100° C. to 250° C., and preferably ranges from 150° C. to 245° C.

The diol modifier included in the composition is selected from the groupconsisting of neopentanediol, 1,3-dihydroxy-2-methylpropane,1,3-dihydroxy-2-methylpropane alkoxylate, 2,5-dimethyl-2,5-hexanediol,polyethylene glycol, and combinations thereof. Preferably, the diolmodifier is used in an amount ranging from 2 to 40 mol %, morepreferably from 5 to 15 mol %, based on total moles of ethylene glycol.

Additionally, the composition may further include a diacid modifier thatis selected from the group consisting of IPA, itaconic acid, adipic acidand combinations thereof. Preferably, the diacid modifier is IPA. Thediacid modifier is used in an amount ranging from 2 to 20 mol %, basedon total moles of terephthalic acid.

The substrate 10 of the high frequency-weldable sheet 1 may be made froma thermoplastic resin. Preferably, the high frequency-weldable sheet 1is a multi-layered laminate. More preferably, the substrate 10 of thehigh frequency-weldable sheet 1 is made from a thermoplastic resinselected from the group consisting of PET, polycarbonate, thermoplasticpolyurethane, nylon and combinations thereof. Most preferably, thesubstrate 10 of the high frequency-weldable sheet 1 is made from PET.

Preferably, the high frequency-weldable sheet 1 further includes asecond high frequency-weldable layer 12 formed on the substrate 10 suchthat the substrate 10 is sandwiched between the first and second highfrequency-weldable layers 11, 12 to form a tri-ply laminate. Preferably,the first and second high frequency-weldable layers 11, 12 and thesubstrate 10 are co-extruded to form the tri-ply laminate. Preferably,the second high frequency-weldable layer 12 is also made from themodified PET material. In this tri-ply laminate embodiment, the modifiedPET material used for manufacturing the first and second highfrequency-weldable layers 11, 12 preferably has an intrinsic viscosityranging from 0.60 to 0.90, more preferably from 0.70 to 0.90.Preferably, each of the first and second high frequency-weldable layers11, 12 has a weight greater than 3 wt %, and preferably ranging from 3wt % to 20 wt %, based on total weight of the high frequency-weldablesheet 1.

More preferably, the substrate 10 of the high frequency-weldable sheet 1may be made from the modified PET material so that the highfrequency-weldable sheet 1 is wholly formed from the modified PETmaterial.

The high frequency-weldable sheet 1 according to this invention issuitable for manufacturing packaging materials, such as those for foodor and beverages.

The high frequency-weldable yarn according to this invention includesfibers composed of a high frequency-weldable material that is made fromthe modified PET material as disclosed above. The highfrequency-weldable yarn has a melting point ranging from 100° C. to 250°C., preferably ranging from 150° C. to 245° C. Preferably, the modifiedPET material for forming the fibers of the high frequency-weldable yarnaccording to this invention has an intrinsic viscosity ranging from 0.5to 0.8.

Referring to FIG. 2, in one preferred embodiment, the fibers of the highfrequency-weldable yarn 2 according to this invention may be furthercomposed of a thermoplastic material. Preferably, each of the fibers hasa core 21 that is made from the thermoplastic material, and an outerlayer 22 that encloses the core 21 and that is made from the highfrequency-weldable material.

Referring to FIG. 3, in another preferred embodiment, the highfrequency-weldable yarn 3 according to this invention may be formed byblending first fibers 31 composed of the thermoplastic material andsecond fibers 32 composed of the modified PET material. Preferably, thehigh frequency-weldable material is used in an amount ranging from 10 wt% to 100 wt %, based on total weight of the first fibers 31 and thesecond fibers 32. More preferably, the second fibers 32 composed of themodified PET material have a fiber fineness (denier/filament, d/f)ranging from 0.7 to 6.0^(d/f), and a length ranging from 2 mm to 80 mm.The thermoplastic material is preferably selected from the groupconsisting of PET, polybutyleneterephthalate, nylon and combinationsthereof.

The high frequency-weldable yarn 2 (3) according to this invention issuitable for manufacturing filters or interlinings. For example, thehigh frequency-weldable yarn 2 (3) according to this invention may beused for forming cords through cross-lapping, spinning, needling orknitting techniques. Preferably, when the high frequency-weldable yarn 2(3) is used for knitting a non-woven cord, the non-woven cord has abasic weight ranging from 50 to 1000 g/cm².

The modified PET material used for manufacturing the highfrequency-weldable articles, such as sheets 1 or yarns 2 (3), accordingto this invention requires to be dried before processing, so as toreduce water content in the modified PET material and to avoid formationof bubbles during processing. Surprisingly, the modified PET materialused for manufacturing the high frequency-weldable sheet 1 or yarn 2 (3)according to this invention can be dried at a higher temperature thanthat of the conventional CHDM-modified PET material without degradingthe structure of the modified PET material. Particularly, the modifiedPET material used in this invention can be dried under a temperature ashigh as 160° C., thereby saving the operation time required formanufacturing the high frequency-weldable articles.

The modified PET material of this invention is suitable for use inconnecting first and second parts of a high frequency-weldable articleaccording to a method of this invention. The method includes the stepsof: (a) preparing the first and second parts, such as the highfrequency-weldable sheets 1 in such a manner that each of the first andsecond parts has a portion composed of a high frequency-weldablematerial that is made from the modified PET material as described above;(b) applying high frequency electromagnetic radiation to the portions ofthe first and second parts so as to melt the portions of the first andsecond parts; and (c) joining the melted portions of the first andsecond parts. In one preferred embodiment as shown in FIG. 4, two highfrequency-weldable sheets 1 shown in FIG. 1 are welded togetheraccording to the method of this invention by connecting the first highfrequency-weldable layer 11 of one high frequency-weldable sheet 1 toeither one of the first and second high frequency-weldable layers 11, 12of the other high frequency-weldable sheet 1.

Preferably, before step (a) the modified PET material is pre-heated to atemperature higher than 70° C., more preferably ranging from 70° C. to160° C., and most preferably ranging from 100° C. to 160° C.

In addition, the operating parameters suitable for high frequencywelding of the high frequency-weldable articles, such as sheets 1 oryarns 2 (3), according to the method of this invention are: frequency:10 to 200 MHz, power density: 5 to 50 W/cm³, and welding time: 4 to 20seconds.

Many other variations, modifications, and alternative embodiments may bemade in the articles and techniques described, by those skilled in theart, without departing from the concept of the present invention.Accordingly, it should be clearly understood that the articles andmethod referred to in the foregoing description and following examplesare illustrative only and are not intended as limitations on the scopeof this invention.

Example 1 I. Preparation of the Modified PET Material

Terephthalic acid, ethylene glycol and 1,3-dihydroxy-2-methylpropanewere added into a mixing vessel in a molar ratio of 1:1.15:0.10, andwere mixed together to form a paste. 50 ppm of an antioxidant (5.6% ofphosphoric acid, H₃PO₄) was added into the paste. Thereafter, theresultant paste was poured into an esterification reactor. Theesterification reaction was conduced for 7 to 9 hours. A polymerizate(esterified product) was obtained and was subsequently transferred to apolymerization vessel, to which 300 ppm of Sb₂O₃ and 56 ppm of Co (OAc)₂were added as a catalyst. The temperature of the polymerization vesselwas elevated to 285° C. for a period of time until a modified PETmaterial having an intrinsic viscosity ranging from 0.8 to 0.9 wasobtained. The modified PET material thus made has a melting point of227° C., and was diced into pellets.

II. Manufacture of Thermoplastic Sheets

The pellets composed of the modified PET material and prepared accordingto the procedures set forth in part I of this Example and an unmodifiedPET material in a weight ratio of 20:80 were added to an extruder(manufactured by Bruckner Co., trade name D83313-Siegsdorf). Thetemperature of the extruder is set at about 270° C. Two outer layerscomposed of modified PET material, and an interlayer composed ofunmodified PET material and sandwiched between the two outer layers wereco-extruded in the extruder so as to form a high frequency-weldablethermoplastic sheet of a tri-ply structure. The thickness ratio of theinterlayer and the two outer layers was 8:1:1.

III. High Frequency Welding Test

The high frequency-weldable thermoplastic sheet obtained from theprocedures set forth in part II of this Example was subjected to a highfrequency welding test by welding portions thereof via a high frequencywelding machine (a foot pneumatic plastic welding machine, Model no. 4-8KW, manufactured by Jyh Yih Electric Enterprise Co., Ltd., Taiwan). Theparameters used in the test were: frequency: 27.12 MHz, pressure: 5 bar,power density: 40 W/cm³, and welding time: 4 to 10 seconds. The effectof the welded portions of the thermoplastic sheet was examined bymanually peeling the welded portions of the thermoplastic sheet. Thetest results show that the welded portions of the thermoplastic sheetmanufactured by this Example were well bonded and were difficult to bepeeled off. In addition, the welded portions of the thermoplastic sheetremain transparent, and no crystallization was formed therein.

Example 2

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 1, except that the terephthalic acid, ethylene glycoland 1,3-dihydroxy-2-methylpropane used for preparing the modified PETmaterial were in a molar ratio of 1:1.15:0.20. The melting point of themodified PET material thus formed was 208° C. The thermoplastic sheetprepared by this Example was subjected to the high frequency weldingtest. The test results show that the welded portions of thethermoplastic sheet remain transparent, and no crystallization wasformed therein.

Example 3

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 2, except that 2,5-dimethyl-2,5-hexanediol was usedto substitute 1,3-dihydroxy-2-methylpropane. The melting point of themodified PET material thus formed was 240° C. The thermoplastic sheetprepared by this Example was subjected to the high frequency weldingtest. The test results show that the welded portions of thethermoplastic sheet remain transparent, and no crystallization wasformed therein.

Example 4

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 1, except that the modified PET material and theunmodified PET material added to the extruder were in a weight ratio of15:85, and that the thickness ratio of the interlayer and the two outerlayers was 11.3:1:1. The thermoplastic sheet prepared by this Examplewas subjected to the high frequency welding test. The test results showthat the welded portions of the thermoplastic sheet remain transparent,and no crystallization was formed therein.

Example 5

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 1, except that the modified PET material and theunmodified PET material added to the extruder were in a weight ratio of10:90, and that the thickness ratio of the interlayer and the two outerlayers was 18:1:1. The thermoplastic sheet prepared by this Example wassubjected to the high frequency welding test. The test results show thatthe welded portions of the thermoplastic sheet remain transparent, andno crystallization was formed therein.

Example 6

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 1, except that isophthalic acid was added into themixing vessel for preparing the modified PET material. The molar ratioof terephthalic acid, isophthalic acid, ethyleneglycol, and1,3-dihydroxy-2-methylpropane was 1:0.02:1.2:0.16. The melting point ofthe modified PET material thus formed was 226° C. The thermoplasticsheet prepared by this Example was subjected to the high frequencywelding test. The test results show that the welded portions of thethermoplastic sheet remain transparent, and no crystallization wasformed therein.

Example 7

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 6, except that the molar ratio of terephthalic acid,isophthalic acid, ethylene glycol, and 1,3-dihydroxy-2-methylpropane was1:0.02:1.2:0.08. The melting point of the modified PET material thusformed was 218° C. The thermoplastic sheet prepared by this Example wassubjected to the high frequency welding test. The test results show thatthe welded portions of the thermoplastic sheet remain transparent, andno crystallization was formed therein.

Example 8

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 6, except that neopentanediol was used to substitute1,3-dihydroxy-2-methylpropane. The melting point of the modified PETmaterial thus formed was 208° C. The thermoplastic sheet prepared bythis Example was subjected to the high frequency welding test. The testresults show that the welded portions of the thermoplastic sheet remaintransparent, and no crystallization was formed therein.

Example 9

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 8, except that the molar ratio of terephthalic acid,isophthalic acid, ethylene glycol, and neopentanediol was1:0.02:1.2:0.08. The melting point of the modified PET material thusformed was 215° C. The thermoplastic sheet prepared by this Example wassubjected to the high frequency welding test. The test results show thatthe welded portions of the thermoplastic sheet remain transparent, andno crystallization was formed therein.

Example 10

The thermoplastic sheet of this Example was prepared in a manner similarto that of Example 6, except that polyethylene glycol (MW. 1000) wasused to substitute 1,3-dihydroxy-2-methylpropane. The melting point ofthe modified PET material thus formed was 230° C. The thermoplasticsheet prepared by this Example was subjected to the high frequencywelding test. The test results show that the welded portions of thethermoplastic sheet remain transparent, and no crystallization wasformed therein.

Example 11 I. Preparation of the Modified PET Material

The modified PET material was prepared in a manner similar to that ofExample 8, except that the esterification reaction stopped at a pointwhere the intrinsic viscosity of the modified PET material was 0.6 to0.8.

II. Manufacture of a High Frequency Weldable Cord

The pellets composed the modified PET material and prepared according tothe procedures set forth in part I of this Example were laddered to formhigh frequency-weldable fibers having a fiber fineness of 2.0 d×0.51 mm.The high frequency-weldable fibers and pure PET fibers were blendedtogether in a weight ratio of 30:70 to form yarns that were subsequentlyformed into a cord. The basic weight of the cord thus formed was 500g/cm².

III. High Frequency Welding Test

The high frequency welding test of the cord thus formed was conducted inthe same manner as that of Example 1. The test results show that thewelded portions of the thermoplastic cord remain transparent, and nocrystallization was formed therein.

While the present invention has been described in connection with whatis considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretations andequivalent arrangements.

1-11. (canceled)
 12. A high frequency-weldable yarn comprising fiberscomposed of a high frequency-weldable material that is made from amodified polyethylene terephthalate material that is prepared from acomposition comprising terephthalic acid, ethylene glycol and a diolmodifier, said diol modifier being selected from the group consisting ofneopentanediol, 1,3-dihydroxy-2-methylpropane,1,3-dihydroxy-2-methylpropane alkoxylate, 2,5-dimethyl-2,5-hexanediol,polyethylene glycol, and combinations thereof, said highfrequency-weldable yarn having a melting point ranging from 100° C. to250° C.
 13. The high frequency-weldable yarn of claim 12, wherein themelting point of said high frequency-weldable yarn ranges from 150° C.to 245° C.
 14. The high frequency-weldable yarn of claim 12, whereinsaid fibers are further composed of a thermoplastic material.
 15. Thehigh frequency-weldable yarn of claim 14, wherein, based on total weightof said fibers, said high frequency-weldable material is used in anamount ranging from 10 wt % to 100 wt %.
 16. The high frequency-weldableyarn of claim 14, wherein each of said fibers has a core that is madefrom said thermoplastic material, and an outer layer that encloses saidcore and that is made from said high frequency-weldable material. 17.The high frequency-weldable yarn of claim 12, wherein, based on totalmoles of ethylene glycol, said diol modifier is used in an amountranging from 2 to 40 mol %.
 18. The high frequency-weldable yarn ofclaim 17, wherein, based on total moles of ethylene glycol, said diolmodifier is used in an amount ranging from 5 to 15 mol %.
 19. The highfrequency-weldable yarn of claim 12, wherein said composition furthercomprises a diacid modifier selected from the group consisting ofisophthalic acid, itaconic acid, adipic acid, and combinations thereof.20. The high frequency-weldable yarn of claim 19, wherein said diacidmodifier is isophthalic acid.
 21. The high frequency-weldable yarn ofclaim 19, wherein, based on total moles of terephthalic acid, saiddiacid modifier is used in an amount ranging from 2 to 20 mol %. 22.(canceled)
 23. (canceled)